Feed System

ABSTRACT

Transport system for the introduction of biomass into a gasifier comprising: a plug screw that forces the biomass into the gasifier, wherein the plug screw is formed such that the biomass is compressed in order on the one hand for it to be conveyed against a pressure in the gasifier and, on the other hand, to leave the gas and bed material in the gasifier, having a gate valve adjacent to the plug screw and which closes when the plug screw stops so that heat, vapour and gas cannot escape.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT/EP2007/058034 filed Aug. 2,2007, which claims priority of DE 10 2006 039 622.7 filed Aug. 24, 2006,both of which are incorporated by reference.

FIELD OF THE INVENTION

The invention concerns a system for feeding biogenic feedstock into agasifier, more particularly into a pulse gasifier in accordance withapplications DE 10 2006 022 265.2, DE 10 2006 017 355.4, DE 10 2006 017353.8.

BACKGROUND

The development of thermal gasification processes has producedessentially three different types of gasifier, the entrained flowgasifier, the fixed bed gasifier and the fluidized bed gasifier.

Originally, the fixed bed gasifier and the fluidized bed gasifier weredeveloped for the commercial gasification of biomasses.

The Carbo-V method will be illustrated here by way of an example for themany different technical approaches to fixed bed gasification.

Literature for fluidized bed gasification which is a component of thisapplication may be taken from the following reference: “High-TemperatureWinkler Gasification of Municipal Solid Waste”; Wolfgang Adlhoch,Rheinbraun AG, Hisaaki Sumitomo Heavy Industries, Ltd., Joachim Wolff,Karsten Radtke (Speaker), Krupp Uhde GmbH; Gasification TechnologyConference; San Francisco, Calif., USA; Oct. 8-11, 2000; ConferenceProceedings.

Literature for a circulating fluidized bed in a network system may betaken from the following sources: “Decentralized heat and powergeneration based on biomass gasification”; R. Rauch, H. Hofbauer;Presentation at University of Leipzig 2004. “Circulating fluidized bed,gasification using air,

Operation Experience with CfB-Technology for Waste, Utilisation at aCement Production Plant” R. Wirthwein, P. Scur, K.-F.Scharf-Rüdersdorfer Zement GmbH, H. Hirschfelder-Lurgi Energie undEntsorgungs GmbH; 7th. International Conference on Circulating FluidizedBed Technologies; Niagara Falls, May 2002.

Literature for the combination fixed bed (rotating tube) can be takenfrom the following sources: 30 MV Carbo V Biomass Gasifier for MunicipalCHP; The CHP Project for the City of Aachen, Matthias Rudloff;Presentation Paris, October 2005

Literature for combination fixed bed gasification (slagging gasifier)can be taken from the following sources: Operation Results of the BGLGasifier at Schwarze Pumpe, Dr. Hans-Joachim Sander SVZ, Dr. GeorgDaradimos, Hansjobst Hirschfelder, Envirotherm; GasificationTechnologies 2003; San Francisco Calif., Oct. 12-15 2003; ConferenceProceedings

Gasification takes place over two stages in the Carbo-V process. Firstthe biomass is split into its volatile and solid constituents at 500° C.This results in a gas containing tar and also “char”. The gas is burntat temperatures in excess of 1200° C., which breaks down the tars intoCO2 and H2. A synthesis gas containing CO and H2 is then generated fromthe hot flue gas and the char.

These types of gasifier are completely unsuited to the gasification ofbiomass (which occurs regionally and has a significant influence on thecosts in terms of logistics and processing) because of the greattechnical effort and high economic costs demanded by the high pressurelevel (up to 40 bar).

Fluidized bed gasifiers may be subdivided into two processes whichdiffer in the heating of the fluidized bed, the circulating fluidizedbed gasifier and the bubbling fluidized bed gasifier.

Literature relating to desulphurization in fluidized bed gasificationcan be found in the following source: Gasification of Lignite and Woodin the Lurgi Circulating Fluidized Bed Gasifier; Research Project2656-3; Final Report, August 1988, P. Mehrling, H. Vierrath; LURGI GmbH;for Electric Power Research Institute, Palo Alto, Calif.:ZWS-Druckvergasung im Kombiblock, Schlussbericht (Circulating fluidizedbed high-pressure gasification in a combiblock, final report) BMFT FB 03E 6384-A; P. Mehrling, LURGI GmbH; Bewag

An allothermal circulating fluidized bed gasification plant was broughton stream at the start of 2002 in Güssing (Austria). The biomass isgasified in a fluidized bed using steam as the oxidizing agent. Aproportion of the char created in the fluidized bed is burnt in a secondfluidized bed to provide the heat for the gasification process. Asynthesis gas is generated by gasification in steam. The disadvantagesare the high acquisition costs for the process engineering and excessivecosts for process control.

The management of the fluidized bed material demands a specificregulation and control system for steam circulation in the form of angas lift pump motion to enhance the exchange of heat and material and toimprove the reaction conditions by increasing the effective reactionspace. The gas lift pump is a materials handling device in which solidmatter/water mixtures are conveyed with the help of compressed air(driving or conveying gas) for instance by means of the injection ofthis gas through nozzles in pipework or in a stirred tank. The injectedgas causes a reduction in the suspension density and hence an increasein buoyancy. Together with the added kinetic energy, this results inconveyance.

A circulation flow results in the containers as the flow.

This is thus transferred to the solids/gas suspension of the fluidizedbed.

This principle is transmitted in the present case to the gas/solidssuspension of the fluidized bed in the steam converter.

All these systems require a transport system to deliver the biogenicfeedstock to the gasifier. The invention below describes a systemcomprising the processes for delivering the biogenic feedstock into agasifier, in particular into a pulse gasifier.

The feedstock covers a broad palette. These may be extruded material,round pellets such as are created by pelleting machines, for instance,or biogenic media from agriculture (cereals).

Characteristic for these biomasses are carbon contents in the originalmaterial in the range of 40 to 50% by mass with hydrogen contents in therange up to 6% by mass and oxygen contents in the range from 40 to 50%by mass. The calorific values of the feedstock are typically in therange up to 20 MJ/kg. The bulk material densities vary over the rangefrom 200 to 700 kg/h. In addition to a certain proportion of fines,extruded materials have a diameter between 5 and 10 mm with a lengthfrom 10 to 20 mm and lump material has dimensions in the area of 20×30mm with a thickness of up to 10 mm.

SUMMARY OF THE INVENTION

An embodiment of the invention provides a transport system whichdelivers the biomass to the reactor efficiently taking intoconsideration the particular characteristics of the reactor.

The process sequence comprises the following steps that are performedwith the appropriate equipment.

a. Buffer:

Buffering in a silo (bunker) as a prior step to feeding and metering.Feedstock from different stores may be conveyed to this buffer.

b. Metering and Feeding to the Points of Delivery into the Gasifier:

Taking the net gas production acting as a setpoint value as a basis(result from the control regime for the steam reforming gasifier), thefeedstock is metered and distributed to one, two or more points ofdelivery such that the gas production required results. The system alsoprovides the function of the plug screw which acts as a pressure sealfor the reactor system. The system has the flexibility to fulfil thesetasks while the broad range of feedstock is being used.

c. Sealing the Reaction System Against the Atmosphere:

A pressure seal for the reactor provided by the material plug formed inthe plug screw and a multi-stage system of cellular wheel feeder andgate valve before and after the plug screw and pressurizing the feedtube with N2 (nitrogen) or CO2 (carbon dioxide) may be necessarydepending on the reactor type.

This material plug is continuously created in the plug screw which actsas the feed device for the gasifier by adjustment of the volumes. Thefeed screws are controlled so that the mass flow and the permanentformation of the sealing plug is ensured.

This system is furthermore characterised in that the plug screw(s)is/are equipped in their forward section with a system of nozzlesoperating in a similar fashion to a jet pulse system, as is known fromfilter technology.

The plug screw is further equipped with cooling devices for the shaftand the jacket. (It is optionally possible to cool the shaft vanes onthis plug screw).

d. Prevention of the Return Flow of the Fluidized Bed Material into theFeed and Metering System when the System is at a Standstill and when theFeed and Metering System is not Operating:

When the gasifier is operating the material is fed into a dense,fluidized bed. Measures are taken to prevent the backflow of bedmaterial into the plug screw when the feed screw is at a standstill,particularly in the start up and shut down processes. To this end, thesystem is equipped with a gate valve that operates through the materialbeing conveyed and shuts off the flow in a suitable manner. Thisequipment also permits the plug screw(s) to be drained through adrainage arrangement as a precaution against the sort of backfires thatcannot be excluded in the case of brief shutdowns of the otherwise hotgasifier.

Thanks to these various aspects, the system is suited to transportinginto the reactor all feedstock coming into consideration forgasification. Because of its particular characteristics, the system isalso capable of feeding into internal pressures up to 5 bar.

It is clear from the above that the feed and metering system comprises,in a preferred embodiment of the following elements:

-   -   a buffer with regulated discharge unit;    -   a metering screw(s) that doses the volume fetched from the        buffer;    -   a transport screw to transport the material to the plug screw;    -   a cellular wheel feeder, gate valve before and after a plug        screw and a plug screw.

The volume of gas produced depends on (is proportional to) the volume offeedstock. This physical dependency is used as a control for the volumefed. Measurement of the volume of syngas, or the comparison between thesetpoint value specification and the volume of syngas measured, is usedas the managing closed loop control for the volume of feedstock. As maybe seen from the drawings, these variables act directly on the meteringscrew (single, parallel or multiple arrangement). This screw/thesescrews is/are fed under the control of the discharge and metering screwfrom the buffer bunker and these control elements too are incorporatedin the control loop together with a fill level monitor in the feed chuteto the metering screw(s).

The following transport screws, not regulated in one possibleembodiment, convey the feedstock to the actual feed system.

The full control loop concept thus comprises feeding biogenic feedstockinto a gasifier for allothermal gasification with the heat of reactionfor the gasification reaction being generated in special pulse burners.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic overview of the invention;

FIG. 2 shows the schematic structure of the metering screw and the plugscrew;

FIG. 3 shows the plug screw in detail.

PREFERRED EMBODIMENTS

The control concept comprises the specification by the volume ofsynthesis gas for metering the feedstock through regulated dischargefrom a buffer and speed-regulated metering screws with monitoring of thefill level of the supply chutes, distribution to the feed devices andformation of the shut-off plugs in the speed-regulated feed screws, withtheir speed being regulated by the master controller and the fill levelmonitoring in the supply to the feed system. This feed system (forsolids) constitutes substantial progress in fluidized bed gasification.

The discharge system 1 (FIG. 1) comprises a screw 3, the rotation speedof which is regulated by the master controller 2, and which is mountedcentrally in the buffer bunker 4. The entire screw is moved over thesilo base by means of a rotary drive 5, itself also speed-regulated.Speed regulation is configured such that the fill level of this screw ismaintained at a constant level by the screw turning into the materialheld in the silo. This means that the delivery rate is directlyproportional to the speed of rotation of the screw and hence thisdischarge system is suitable for feed regulation. The currentconsumption of the rotatably mounted screw that is directly proportionalwith the torque of this screw is used as the reference variable for thespeed control.

The volume is determined by the master control as a function of thesetpoint value for the synthesis gas 7 by means of a metering screw. Thevolume fetched from the buffer silo is metered accordingly.

One or more transport screws 8 transport the volume to the plug screws9.

The feed system comprises a cellular wheel 10, gate valve 11 upstream ofthe screw for onwards conveying and simultaneously shutting off both instart-up and shut-down operation and for feeding the plug screw 9. Thesystem is equipped with a system 12 (see FIG. 3) for pressurizing itwith air as a sealing medium and/or an inert gas such as N2 or CO2 orsteam (the latter medium also acting as an extinguishing and sealingmedium). As is clear from FIG. 2, the system comprises the plug screwitself, in which the material plug is generated to plug the pressure.The screw is designed such that this material plug remains stable acrossthe entire speed range and hence with variable volumes of feedstock.This feedstock is conveyed directly into the hot fluidized bed via thegate valve that remains open during operation through a smooth, heatresistant pipe.

Furthermore, the screw includes cooling equipment 13, 14 for cooling thescrew shaft 14 and optionally the screw vanes and the jacket 13 in whichthe screw is fitted. This can be shaft cooling and jacket cooling.

One part of the system is the gate valve 15 directly between the feedscrew and the gasifier 16 that is closed when the screw is shut down andprevents the inert bed material flowing back into the screw.

This gate valve is made from heat resistant material as it is located atthe interface between the gasifier which is hot in operation and thecooled screw. This measure also prevents backflow during the operationalphases in which the feedstock plug being fed does not itself establishthe isolation.

The feedstock is supplied to the feed screw by way of a chute 17,cellular wheel feeder 10 and gate valve 11. The fill level monitoring 18in this feed line guarantees the necessary permanent formation of amaterial plug for the feedstock throughput configured through the maincontrol system. The arrangement of the cellular wheel feeder and gatevalve upstream of the screw furthermore permits the introduction of asealing gas (air or inert gases such as CO2, nitrogen or steam inexceptional cases).

Gate valve 11 permits an additional gas-tight seal.

A pressure range of the reaction system of up to 5 bar overpressure, asa rule 1.5 bar overpressure, is hence controllable.

1. Transport system for the introduction of biomass into a gasifiercomprising: a plug screw that forces the biomass into the gasifier,wherein the plug screw is formed such that the biomass is compressed inorder on the one hand for it to be conveyed against a pressure in thegasifier and, on the other hand, to leave the gas and bed material inthe gasifier, having a gate valve adjacent to the plug screw and whichcloses when the plug screw stops so that heat, vapour and gas cannotescape.
 2. The transport system according claim 1, wherein a coolingsystem cools the plug screw from the inside or the outside.
 3. Thetransport system according claim 1, wherein one gate valve is arrangedupstream of the plug screw and one gate valve is arranged downstream ofit.
 4. The transport system according claim 1, whereby a cellular wheelfeeder is mounted before the plug screw onto which a feed chute abuts.5. The transport system according claim 1, whereby the plug screw isequipped in its forward area with a system of nozzles that operates in asimilar fashion to a jet pulse system.
 6. The transport system accordingclaim 1, whereby a sealing gas may be introduced into the casing of theplug screw, more particularly N2 (nitrogen) or CO2 (carbon dioxide) issupplied to the injection tube.
 7. The transport system according claim1, whereby a buffer that operates with a regulated discharge unit, isconnected upstream of the plug screw.
 8. The transport system accordingclaim 1, whereby the discharge system comprises a screw mountedcentrally in the buffer silo and regulated by a controller.
 9. Thetransport system according claim 8, whereby the entire screw can bemoved over the floor of the bunker, also by means of a speed-regulatedrotary drive.
 10. The transport system in accordance with claim 1,whereby one or more metering screw(s) meter the biomass that is fetchedfrom the buffer bunker and, where necessary a transport screw transportsthe biomass to the plug screw.
 11. The transport system i accordingclaim 1, whereby a control unit that calculates the volume of gasproduced proportionally to the feedstock so that this physicaldependence can be used as a control for the volume of material fed sothat the measurement of the synthesis gas volume, or the comparisonbetween the specified value and the measured volume of syngas producedmay be used as the managing control for the volume of feedstock. 12.Method for the introduction of biomass into a gasifier comprising:introducing of the biomass by way of a plug screw whereby the plug screwis regulated such that the biomass is compressed in order on the onehand for it to be conveyed against a pressure in the gasifier and, onthe other hand, to leave the gas and bed material in the gasifier,Closing of a gate valve adjacent to the plug screw and which closes ifthe plug screw stops so that heat, vapour and gas cannot escape.
 13. Themethod according claim 12, wherein a cooling system cools the plug screwfrom the inside or the outside.
 14. The method according claim 12whereby one gate valve is mounted upstream of the plug screw and one ismounted downstream of it and these are closed as a function of thesupply or removal of the biomass.
 15. The method according to claim 12whereby a cellular wheel feeder is mounted upstream of the plug screwonto which a feed chute abuts wherein the feeder is controlled such thatthe plug screw is continuously supplied with biomass.
 16. The methodaccording claim 12 whereby the plug screw is equipped in its forwardarea with a system of nozzles that operates in a similar fashion to ajet pulse system to inject into the biomass.
 17. The method accordingclaim 12 whereby a sealing gas is introduced into the jacket of the plugscrew, more particularly N2 (nitrogen) or CO2 (carbon dioxide) issupplied under pressure to an injection tube to prevent the occurrenceof a drop in pressure.
 18. The method according claim 12 whereby theplug screw is supplied from a buffer by a regulated discharge unit. 19.The method according claim 12, whereby the discharge system comprises ascrew mounted centrally in the buffer silo and regulated by acontroller.
 20. The method according claim 19, whereby the entire screwis moved over the floor of the bunker, also by means of aspeed-regulated rotary drive.
 21. The method system according claim 12,whereby one or more metering screw(s) meter the volume that is fetchedfrom the buffer bunker and, where necessary a transport screw transportsthe biomass to the plug screw.
 22. The method according claim 12 wherebya control unit calculates the volume of gas produced proportionally tothe feedstock so that this physical dependence can be used as a controlfor the volume of material fed so that the measurement of the synthesisgas volume, or the comparison between the specified value and themeasured volume of syngas produce may be used as the managing controlfor the volume of feedstock.